Attempting to send analog data from Spark Core to Thingspeak. (Note: Something still not fully working. First post works, then it hangs.)

gistfile1.txt

// ThingSpeak Settings
char thingSpeakAddress[] = "api.thingspeak.com";
String writeAPIKey = "THINGSPEAK_WRITE_API";
const unsigned int updateThingSpeakInterval = 30000; 

unsigned long lastConnectionTime = 0; 
bool lastConnected = false;
int failedCounter = 0;

TCPClient client;

void setup()
{
  Serial.begin(9600);
  delay(1000);
}

void loop()
{
  // Read value from Analog Input Pin 0
  String analogPin0 = String(analogRead(A0), (unsigned char) DEC);
  
  // Print Update Response to Serial Monitor
  if (client.available())
  {
    char c = client.read();
    Serial.print(c);
  }

  // Disconnect from ThingSpeak
  if (!client.connected() && lastConnected)
  {
    Serial.println("...disconnected");
    Serial.println();
    
    client.stop();
  }
  
  // Update ThingSpeak
  if(!client.connected() && (millis() - lastConnectionTime > updateThingSpeakInterval))
  {
    updateThingSpeak("field1="+analogPin0);
  }
  
  lastConnected = client.connected();
}

void updateThingSpeak(String tsData)
{
  if (client.connect(thingSpeakAddress, 80))
  {         
    client.print("POST /update HTTP/1.1\n");
    client.print("Host: api.thingspeak.com\n");
    client.print("Connection: close\n");
    client.print("X-THINGSPEAKAPIKEY: "+writeAPIKey+"\n");
    client.print("Content-Type: application/x-www-form-urlencoded\n");
    client.print("Content-Length: ");
    client.print(tsData.length());
    client.print("\n\n");

    client.print(tsData);
    
    lastConnectionTime = millis();
    
  }
  else
  {
    Serial.println("Connection to ThingSpeak Failed: disconnecting"); 
    client.stop();
  }
}